The present invention relates to a shaft position detection sensor which decreases erroneous detections due to grease coated on a shaft. The shaft position detection sensor magnetically detects a position on the shaft which is constructed in such a manner that a permeability or a cross section area of a detection portion to be detected is different from the other portions.
In the case that a position on a ball screw is detected in a movement mechanism using a ball screw and a ball nut, a position detection sensor as described later has been known. An optical sensor is provided on the ball nut while a portion where a reflectance rate being different from other portions is provided on a certain portion of the ball screw, so that the strength of the reflection light is detected.
However, in such position sensor optically detecting the position, it is necessary to place the detecting unit extremely close to the ball screw. Therefore, the optical detection unit may be dirty due to grease coated on a surface of the ball screw. As described above, detection accuracy may be deteriorated.